\Ox*al"ic\, a. [From {Oxalis}: cf. F. oxalique.] (Chem.)
Pertaining to, derived from, or contained in, sorrel, or
oxalis; specifically, designating an acid found in, and
characteristic of, oxalis, and also certain plant of the
Buckwheat family.
{Oxalic acid} (Chem.), a dibasic acid, existing combined in
   oxalis as an acid potassium oxalate, and in many plant
   tissues as the calcium oxalate. It is prepared on a large
   scale, by the action of fused caustic soda or potash on
   sawdust, as a white crystalline substance, which has a
   strong acid taste, and is poisonous in large doses. It is
   used in dyeing, calico printing, bleaching flax and straw,
   the preparation of formic acid, and in salts of lemon for
   removing ink stains, mold, etc.